Federal Aviation Administration Regulations require an aircraft to include position (or navigation) lights which help identify the attitude and position of the aircraft to nearby airborne and land-based entities. More specifically, airplanes are required to have left and right position lights consisting of a red light and a green light spaced laterally as far apart as practical, and installed on the airplane such that, when the airplane is in normal flying position, the red light is on the left side of the airplane and the green light is on the right side of the airplane. Additionally, airplanes must have a rear position light which is a white light mounted as far aft as practical on the tail or on each wingtip of the airplane.
Most airplane manufacturers comply with these regulations by installing position lights on airplanes that are implemented through the use of incandescent light sources. Alternatively, some position lights operate through the use of halogen lamps, which can have a longer life expectancy than incandescent lamps. These two types of light sources are often utilized because they can achieve the light distribution and light intensity required by Federal Aviation Regulations, promulgated by the Federal Aviation Administration (FAA). The FAA requires position lights to be of a minimum intensity at a multitude of displacement angles in both horizontal and vertical planes, as defined by an airplane's orientation. Regulations also require that position lights may not exceed specific light intensity values in certain horizontal and vertical positions. That is, within a position light's intended field of coverage, the FAA establishes minimum intensities only, and outside the intended field of coverage, the FAA establishes maximum intensities. In this manner, an airplane's attitude and position can easily be determined from multiple viewing angles while at the same time insuring that the lights are not too intense beyond the position lights' field of coverage to confuse or overpower other pilots, aircraft lights, and ground-based entities.
In addition to horizontal and vertical light intensity requirements, Federal Aviation Regulations also require each position light to be of a specific color based upon International Commission on Illumination chromaticity coordinates. Federal Aviation Regulations use these chromaticity coordinates to define a particular range of chromaticities or colors suitable for position lights, defined as aviation red, aviation green, and aviation white. The left position light must be aviation red, the right position light must be aviation green, and the rear position light must be aviation white.
Because most position lights use white incandescent and halogen light sources, position light manufacturers often achieve these particular color requirements through the use of light covers. Light covers are typically made of colored glass, and are placed in front of the light source. However, the use of these covers in flight conditions and with incandescent or halogen light sources can result in undesired consequences. For example, the transmittance of red and green glass covers is only about 20 percent. This results in the use of a relatively high powered lamp to meet light intensity requirements. High powered incandescent and halogen light sources emit a large amount of heat, which can shatter light covers made of glass. Furthermore, light covers can change color and transmittance with temperature, so that light intensity and color may fluctuate outside of specified Federal Aviation Regulation requirements in response to temperature variations.
Because position lights must operate each time an aircraft is operating at night and because the lights can be difficult to access, especially on large commercial aircraft, it is advantageous for position lights to have long life and to perform reliably. Unfortunately, however, position lights which use conventional incandescent and halogen lamps can typically burn out after 1000 to 2000 hours of operation. This can occur at an inopportune time, such as in-flight or during a short layover on a runway. As a result, the lamps inside these position lights are frequently replaced while the airplane is on the tarmac. This frequent lamp replacement represents a high burden to airplane operators, maintenance crews, air traffic control, and any passenger or cargo on the airplane.
In addition to costs associated with aircraft delays and required maintenance, conventional light sources used in combination with colored filtered glass require a large power supply and can be very heavy, both of which are undesirable in airplane design. In this regard, incandescent and halogen position lights each require about 150-200 watts of power to produce intensity to meet FAA lighting requirements with suitable margin and redundancy. For example, 100-200 watt position lights are typically employed to provide twice the light intensity required under Federal Aviation Regulations. With multiple position lights on each airplane, this high power requirement contributes to a large power load, which is undesirable because of the limitations of the generators on an aircraft. Furthermore, the heavy weight of incandescent and halogen position lights and light covers make the lights difficult to install, and add to undesirable weight to the aircraft. Finally, (red and white) incandescent and halogen position lights emit light having a broad spectrum and relatively high amount of infrared energy, making the lights interfere with night vision imaging systems (NVIS), such as employed in military and night rescue applications.
Accordingly, there is a continuing need for a reliable position light which results in a longer life and requires less maintenance than conventional position lights, while achieving FAA light intensity and distribution requirements. Furthermore, it is desirable for such a light to have reduced power consumption and reduced manufacturing costs, to be lightweight, and to have a narrow spectral distribution and lower infrared energy than conventional position lights, thereby allowing for compatibility with night vision imaging systems.